1. Field of the Invention
This invention relates generally to the pushbutton of a switch which is to be operated by an adjustably positioned screw and, more particularly, to a pushbutton design which engages the central portion of the adjusting screw thereby to provide more precise adjustment control.
2. Description of the Prior Art
The present invention is essentially a new button construction for a switch to be operated by a mechanical device wherein the final linkage is an adjusting screw which engages the end of the button to operate the switch. In mechanical switching devices, especially where a number of gears are involved in the switching action, adjustment of the switch activator to activate the switch over a particular portion of the operating cycle is accomplished by use of an adjustably positioned threaded screw. An example of such an arrangement is shown in U.S. Pat. No. 4,094,396 to Greenwald.
The device in U.S. Pat. No. 4,094,396 is a control device for a coin-operated mechanism such as would be used to control the duration of the operating cycle of automatic coin-operated clothes washers and dryers. Timing control allows adjustment of the effective cost of operating the mechanism by controlling the duration of the operating cycle. In order to control the timing cycle of the control device, an arrangement in the form of an adjusting screw passes through a tapped hole in a pivotally mounted lever arm to engage the pushbutton of a snap-action switch. The lever arm is moved by a ratchet wheel arrangement which, in turn, is driven by a timing mechanism. By rotating the screw in its tapped hole or socket, fine adjustment of the actuation of the switch by the timing device is accomplished.
The adjustment screw is typically one formed by rolling a thread on a screw blank. This results in a screw which has an uneven end edge with discontinuities of at least 5/1000ths of an inch. This is inherent in the manufacturing process. Because of the uneven end, contact between the screw and the top of the pushbutton changes from position to position on both the end of the screw and the pushbutton, and can change the time adjustment in a discontinuous manner by at least 4-5 minutes in a typical mechanism. In a timing cycle of sixty minutes, a variation of 4 minutes is substantial and undesirable.
It is therefore an object of the present invention to provide an engagement structure to avoid the disadvantages of the prior art and provide more precise adjustability of the switching structure.